Let me preface this by stating I leave on my 4g, GPS, run in performance mode and don't kill tasks. I initially purchased the extended battery but ran the stock battery just to see if I even needed the extended one. The stock battery life is abysmal. I couldn't squeeze 8 full hours out of it. Having switched to the extended I'm running at least 24 hours with moderate/heavy usage. I have to warn anyone interested in the extended battery that it adds a good deal of heft and size to the phone. I personally don't care and will take the added life and use of the phone over the added dimensions etc.
Sent from my HTC Rezound